v3.25.4

Schedule III: Real Estate and Accumulated Depreciation - Schedule (Details) - USD ($) $ in Thousands | 12 Months Ended |  |  |
--- | --- | --- | --- | ---
Dec. 31, 2025 | Dec. 31, 2024 | Dec. 31, 2023 | Dec. 31, 2022
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation |  |  |  |
Encumbrances | $ 836,691 |  |  |
Initial cost of Land | 19,206 |  |  |
Initial cost of Building and Leasehold improvements | 24,435 |  |  |
Costs capitalized subsequent to acquisition | 1,060,130 |  |  |
Carrying amount of Land | 32,271 |  |  |
Carrying amount of Buildings and Leasehold improvements | 1,069,350 |  |  |
Development and Construction in progress | 2,150 |  |  |
Total | 1,103,771 | $ 1,085,197 | $ 1,066,620 | $ 1,084,598
Accumulated Depreciation and Amortization | 473,141 | 443,627 | $ 415,903 | $ 396,268
Net basis difference of assets and liabilities between tax basis and GAAP basis | 125,793 |  |  |
Mortgages |  |  |  |
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation |  |  |  |
Deferred debt issuance costs, net | 7,240 | $ 8,525 |  |
Rego Park I |  |  |  |
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation |  |  |  |
Encumbrances | 0 |  |  |
Initial cost of Land | 1,647 |  |  |
Initial cost of Building and Leasehold improvements | 8,953 |  |  |
Costs capitalized subsequent to acquisition | 92,735 |  |  |
Carrying amount of Land | 1,647 |  |  |
Carrying amount of Buildings and Leasehold improvements | 99,538 |  |  |
Development and Construction in progress | 2,150 |  |  |
Total | 103,335 |  |  |
Accumulated Depreciation and Amortization | $ 51,777 |  |  |
Date of Construction | 1959 |  |  |
Date acquired | 1992 |  |  |
Rego Park I | Minimum |  |  |  |
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation |  |  |  |
Life on which Depreciation in Latest Income Statement is Computed | 3 years |  |  |
Rego Park I | Maximum |  |  |  |
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation |  |  |  |
Life on which Depreciation in Latest Income Statement is Computed | 39 years |  |  |
Rego Park II |  |  |  |
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation |  |  |  |
Encumbrances | $ 175,000 |  |  |
Initial cost of Land | 3,127 |  |  |
Initial cost of Building and Leasehold improvements | 1,467 |  |  |
Costs capitalized subsequent to acquisition | 420,795 |  |  |
Carrying amount of Land | 3,127 |  |  |
Carrying amount of Buildings and Leasehold improvements | 422,262 |  |  |
Development and Construction in progress | 0 |  |  |
Total | 425,389 |  |  |
Accumulated Depreciation and Amortization | $ 159,224 |  |  |
Date of Construction | 2009 |  |  |
Date acquired | 1992 |  |  |
Rego Park II | Minimum |  |  |  |
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation |  |  |  |
Life on which Depreciation in Latest Income Statement is Computed | 3 years |  |  |
Rego Park II | Maximum |  |  |  |
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation |  |  |  |
Life on which Depreciation in Latest Income Statement is Computed | 40 years |  |  |
The Alexander apartment tower |  |  |  |
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation |  |  |  |
Encumbrances | $ 94,000 |  |  |
Initial cost of Land | 0 |  |  |
Initial cost of Building and Leasehold improvements | 0 |  |  |
Costs capitalized subsequent to acquisition | 115,501 |  |  |
Carrying amount of Land | 0 |  |  |
Carrying amount of Buildings and Leasehold improvements | 115,501 |  |  |
Development and Construction in progress | 0 |  |  |
Total | 115,501 |  |  |
Accumulated Depreciation and Amortization | $ 33,557 |  |  |
Date of Construction | 2016 |  |  |
Date acquired | 1992 |  |  |
The Alexander apartment tower | Minimum |  |  |  |
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation |  |  |  |
Life on which Depreciation in Latest Income Statement is Computed | 3 years |  |  |
The Alexander apartment tower | Maximum |  |  |  |
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation |  |  |  |
Life on which Depreciation in Latest Income Statement is Computed | 39 years |  |  |
Flushing |  |  |  |
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation |  |  |  |
Encumbrances | $ 0 |  |  |
Initial cost of Land | 0 |  |  |
Initial cost of Building and Leasehold improvements | 1,660 |  |  |
Costs capitalized subsequent to acquisition | (107) |  |  |
Carrying amount of Land | 0 |  |  |
Carrying amount of Buildings and Leasehold improvements | 1,553 |  |  |
Development and Construction in progress | 0 |  |  |
Total | 1,553 |  |  |
Accumulated Depreciation and Amortization | $ 1,454 |  |  |
Date of Construction | 1975 |  |  |
Date acquired | 1992 |  |  |
Lexington Avenue |  |  |  |
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation |  |  |  |
Encumbrances | $ 567,691 |  |  |
Initial cost of Land | 14,432 |  |  |
Initial cost of Building and Leasehold improvements | 12,355 |  |  |
Costs capitalized subsequent to acquisition | 431,206 |  |  |
Carrying amount of Land | 27,497 |  |  |
Carrying amount of Buildings and Leasehold improvements | 430,496 |  |  |
Development and Construction in progress | 0 |  |  |
Total | 457,993 |  |  |
Accumulated Depreciation and Amortization | $ 227,129 |  |  |
Date of Construction | 2003 |  |  |
Date acquired | 1992 |  |  |
Lexington Avenue | Minimum |  |  |  |
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation |  |  |  |
Life on which Depreciation in Latest Income Statement is Computed | 9 years |  |  |
Lexington Avenue | Maximum |  |  |  |
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation |  |  |  |
Life on which Depreciation in Latest Income Statement is Computed | 39 years |  |  |

X
- Definition Net Basis Difference Of Assets And Liabilities Between Tax Basis And GAAP Basis + References No definition available. + Details
Name: | alx_NetBasisDifferenceOfAssetsAndLiabilitiesBetweenTaxBasisAndGAAPBasis
Namespace Prefix: | alx_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition The carrying amount at which development and construction in progress are carried at the end of the period. + References No definition available. + Details
Name: | alx_RealEstateAndAccumulatedDepreciationCarryingAmountOfDevelopmentAndConstructionInProgress
Namespace Prefix: | alx_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Date real estate investment property was acquired for entities with a substantial portion of business acquiring and holding investment real estate, in CCYY format. + References No definition available. + Details
Name: | alx_RealEstateAndAccumulatedDepreciationYearAcquired
Namespace Prefix: | alx_
Data Type: | xbrli:gYearItemType
Balance Type: | na
Period Type: | duration

X
- Definition Date real estate investment property was constructed for entities with a substantial portion of business acquiring and holding investment real estate, in CCYY format. + References No definition available. + Details
Name: | alx_RealEstateAndAccumulatedDepreciationYearOfConstruction
Namespace Prefix: | alx_
Data Type: | xbrli:gYearItemType
Balance Type: | na
Period Type: | duration

X
- Definition Amount of lien or mortgage outstanding on real estate investment properties for entities with a substantial portion of business acquiring and holding investment real estate. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name Regulation S-X (SX) -Number 210 -Section 12 -Subsection 28 -Paragraph Column B -Publisher SEC Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 970 -SubTopic 360 -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.12-28(Column B)) -Publisher FASB -URI https://asc.fasb.org/1943274/2147478979/970-360-S99-1 + Details
Name: | srt_RealEstateAndAccumulatedDepreciationAmountOfEncumbrances
Namespace Prefix: | srt_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name Regulation S-X (SX) -Number 210 -Section 12 -Subsection 28 -Paragraph Column A -Footnote 2 -Publisher SEC Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Name Regulation S-X (SX) -Number 210 -Section 12 -Subsection 28 -Paragraph Column I -Publisher SEC Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Name Regulation S-X (SX) -Number 210 -Section 12 -Subsection 28 -Paragraph Column H -Publisher SEC Reference 4: http://www.xbrl.org/2003/role/disclosureRef -Name Regulation S-X (SX) -Number 210 -Section 12 -Subsection 28 -Paragraph Column G -Publisher SEC Reference 5: http://www.xbrl.org/2003/role/disclosureRef -Name Regulation S-X (SX) -Number 210 -Section 12 -Subsection 28 -Paragraph Column F -Publisher SEC Reference 6: http://www.xbrl.org/2003/role/disclosureRef -Name Regulation S-X (SX) -Number 210 -Section 12 -Subsection 28 -Paragraph Column E -Publisher SEC Reference 7: http://www.xbrl.org/2003/role/disclosureRef -Name Regulation S-X (SX) -Number 210 -Section 12 -Subsection 28 -Paragraph Column D -Publisher SEC Reference 8: http://www.xbrl.org/2003/role/disclosureRef -Name Regulation S-X (SX) -Number 210 -Section 12 -Subsection 28 -Paragraph Column C -Publisher SEC Reference 9: http://www.xbrl.org/2003/role/disclosureRef -Name Regulation S-X (SX) -Number 210 -Section 12 -Subsection 28 -Paragraph Column B -Publisher SEC Reference 10: http://www.xbrl.org/2003/role/disclosureRef -Topic 970 -SubTopic 360 -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.12-28(Column F)) -Publisher FASB -URI https://asc.fasb.org/1943274/2147478979/970-360-S99-1 Reference 11: http://www.xbrl.org/2003/role/disclosureRef -Topic 970 -SubTopic 360 -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.12-28(Column E)) -Publisher FASB -URI https://asc.fasb.org/1943274/2147478979/970-360-S99-1 Reference 12: http://www.xbrl.org/2003/role/disclosureRef -Topic 970 -SubTopic 360 -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.12-28(Column D)) -Publisher FASB -URI https://asc.fasb.org/1943274/2147478979/970-360-S99-1 Reference 13: http://www.xbrl.org/2003/role/disclosureRef -Topic 970 -SubTopic 360 -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.12-28(Column C)) -Publisher FASB -URI https://asc.fasb.org/1943274/2147478979/970-360-S99-1 Reference 14: http://www.xbrl.org/2003/role/disclosureRef -Topic 970 -SubTopic 360 -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.12-28(Column I)) -Publisher FASB -URI https://asc.fasb.org/1943274/2147478979/970-360-S99-1 Reference 15: http://www.xbrl.org/2003/role/disclosureRef -Topic 970 -SubTopic 360 -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.12-28(Column A)(Footnote 2)) -Publisher FASB -URI https://asc.fasb.org/1943274/2147478979/970-360-S99-1 Reference 16: http://www.xbrl.org/2003/role/disclosureRef -Topic 970 -SubTopic 360 -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.12-28(Column B)) -Publisher FASB -URI https://asc.fasb.org/1943274/2147478979/970-360-S99-1 Reference 17: http://www.xbrl.org/2003/role/disclosureRef -Topic 970 -SubTopic 360 -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.12-28(Column G)) -Publisher FASB -URI https://asc.fasb.org/1943274/2147478979/970-360-S99-1 Reference 18: http://www.xbrl.org/2003/role/disclosureRef -Topic 970 -SubTopic 360 -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.12-28(Column H)) -Publisher FASB -URI https://asc.fasb.org/1943274/2147478979/970-360-S99-1 + Details
Name: | srt_RealEstateAndAccumulatedDepreciationLineItems
Namespace Prefix: | srt_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Amount, after accumulated amortization, of debt issuance costs. Includes, but is not limited to, legal, accounting, underwriting, printing, and registration costs. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 835 -SubTopic 30 -Name Accounting Standards Codification -Section 45 -Paragraph 1A -Publisher FASB -URI https://asc.fasb.org/1943274/2147482925/835-30-45-1A Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 835 -SubTopic 30 -Name Accounting Standards Codification -Section 45 -Paragraph 2 -Publisher FASB -URI https://asc.fasb.org/1943274/2147482925/835-30-45-2 Reference 3: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 835 -SubTopic 30 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Publisher FASB -URI https://asc.fasb.org/1943274/2147482900/835-30-50-1 Reference 4: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 470 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1D -Subparagraph (a) -Publisher FASB -URI https://asc.fasb.org/1943274/2147481139/470-20-50-1D + Details
Name: | us-gaap_DeferredFinanceCostsNet
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Useful life of long lived, physical assets used in the normal conduct of business and not intended for resale, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. Examples include, but not limited to, land, buildings, machinery and equipment, office equipment, furniture and fixtures, and computer equipment. + References No definition available. + Details
Name: | us-gaap_PropertyPlantAndEquipmentUsefulLife
Namespace Prefix: | us-gaap_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | instant

X
- Definition Amount of accumulated depreciation pertaining to real estate investments for entities with a substantial portion of business acquiring and holding investment real estate. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 970 -SubTopic 360 -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.12-28(Column F)) -Publisher FASB -URI https://asc.fasb.org/1943274/2147478979/970-360-S99-1 + Details
Name: | us-gaap_RealEstateAccumulatedDepreciation
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Amount before accumulated depreciation of buildings and improvements for entities with a substantial portion of business acquiring and holding investment real estate. Excludes real estate not held as an investment or interest. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 970 -SubTopic 360 -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.12-28(Column E)) -Publisher FASB -URI https://asc.fasb.org/1943274/2147478979/970-360-S99-1 + Details
Name: | us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsAndImprovements
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amount of land for entities with a substantial portion of business acquiring and holding investment real estate. Excludes real estate not held as an investment or interest. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 970 -SubTopic 360 -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.12-28(Column E)) -Publisher FASB -URI https://asc.fasb.org/1943274/2147478979/970-360-S99-1 + Details
Name: | us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amount of land and buildings and improvements made to real estate investments and capitalized after acquisition for entities with a substantial portion of business acquiring and holding investment real estate. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 970 -SubTopic 360 -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.12-28(Column D)) -Publisher FASB -URI https://asc.fasb.org/1943274/2147478979/970-360-S99-1 + Details
Name: | us-gaap_RealEstateAndAccumulatedDepreciationCostsCapitalizedSubsequentToAcquisitionImprovements
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Initial cost of buildings and improvements for entities with a substantial portion of business acquiring and holding investment real estate. Excludes real estate not held as an investment or interest. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 970 -SubTopic 360 -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.12-28(Column C)) -Publisher FASB -URI https://asc.fasb.org/1943274/2147478979/970-360-S99-1 + Details
Name: | us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfBuildingsAndImprovements
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Initial cost of land for entities with a substantial portion of business acquiring and holding investment real estate. Excludes real estate not held as an investment or interest. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 970 -SubTopic 360 -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.12-28(Column C)) -Publisher FASB -URI https://asc.fasb.org/1943274/2147478979/970-360-S99-1 + Details
Name: | us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amount, before accumulated depreciation, of real estate investment by entity with substantial portion of business acquiring and holding investment real estate or interest in real estate. Excludes real estate not held as investment or interest. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 970 -SubTopic 360 -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.12-28(Column E)) -Publisher FASB -URI https://asc.fasb.org/1943274/2147478979/970-360-S99-1 + Details
Name: | us-gaap_RealEstateGrossAtCarryingValue
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Details
Name: | us-gaap_LongtermDebtTypeAxis=us-gaap_MortgagesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis=alx_RegoPark1PropertyMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_RangeAxis=srt_MinimumMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_RangeAxis=srt_MaximumMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis=alx_RegoPark2PropertyMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis=alx_AlexanderApartmentTowerMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis=alx_FlushingPropertyMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis=alx_LexingtonAvenuePropertyMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |